Well first of all, make sure u set a good port for your server.
Make sure u allow it in windows firewall and in ur router and firewall on pc
U have to forward 29070 for example.. as UDP ..
Just run ur server then. Remember you can't see your own server in the list!www.whatsmyip.com -- get ur ip here and ask a friend to do /connect ip:29070 (or ort -- depends on which port you take)